Positive displacement pump with rotating reciprocating piston and improved lubrication feature

ABSTRACT

A positive displacement pump especially designed for home use comprises a crankcase housing and a cylinder block joined thereto, the cylinder block containing a cylindrical bore whose longitudinal axis is at a predetermined angle relative to the longitudinal axis of the pump&#39;s drive shaft journaled in the crankcase housing. A piston having a central longitudinal bore formed inward from one end thereof and which includes a timing window extending through its side surface, is fitted into the cylindrical bore and coupled to the drive shaft by a pin which is journaled in a spherical bearing. A suction port is formed through the wall of the cylinder block on one side surface thereof and on the opposite side surface, 180° away, is a high pressure discharge port. When the pump is driven, the piston both rotates and reciprocates causing the timing window in the piston to sweep by the inlet or suction port where a charge of liquid at low pressure is allowed to enter the hollow piston. As the piston rotates, the timing window moves to a point where it is ultimately in line with the discharge port when the piston is at a top dead center position. By canting the pin of the piston relative to its longitudinal axis compensation for the unequal hydraulic forces acting in the transverse direction on the piston results. An improved lubrication system incorporating grease as the lubricant is also employed.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates generally to fluid handling equipment, and moreparticularly to an improved, low-cost positive displacement pumpespecially designed for residential high-pressure washing applications.

II. Discussion of the Prior Art

Generally speaking, most municipalities deliver water to residentialestablishments at a pressure of about 60 psi. Such pressure isoftentimes insufficient for such applications as automobile washing,garage floor and driveway cleanup, removing the flaking paint frombuilding sidings and similar applications. End-uses like this requirethat water be delivered at relatively high pressures and at acceptableflow rates such that the momentum of the water striking the surface tobe cleaned will be effective to dislodge the dirt, grease and grime tobe removed. It has been found that a pump delivering water at about1,000 psi and at a flow rate of two gallons/minute is satisfactory formost residential pressure washing applications.

A wide variety of positive displacement pump devices are available whichwill meet such requirements. Single or multiple piston pumps, whendriven by an electric motor or internal combustion engine can readilymeet the pressure and flow rate requirements. However, such pumps, inthe past, have tended to be relatively heavy, fairly complex and,therefore, relatively expensive, making it difficult to sell to averagehomeowners.

For example, applicant's assignee, Hypro Corporation of St. Paul, Minn.,offers a line of single and of multiple piston positive displacementpumps of the type including a crankcase, a cylinder block affixed to thecrankcase, a shaft journaled for rotation in the crankcase having one ormore eccentrics and coupled by an appropriate number of connecting rodsto the piston which is mounted for reciprocal movement within a cylinderbore formed in the cylinder block. Pumps of this type also requiresuitable inlet and outlet poppet valves as well as appropriate sealsoperatively disposed between the cylinder walls and the piston toprevent the liquid being pumped from entering the crankcase and foreffectively isolating the low pressure or suction port from the highpressure discharge port.

To meet the average residential consumer demand for a relatively lowcost, light-weight pump for high pressure washing applications aroundthe home and farm, Hypro Corporation engaged the Southwest ResearchInstitute in San Antonio, Tex., to develop a pump for home use whichwould meet prescribed and rather stringent specifications in terms ofcost and performance. Rather than attempting to cost reduce existingpump designs developed for commercial and industrial applications sothat the resulting product could be more readily marketed to the generalconsumer, it was decided instead to adapt a particular type of pump thatheretofore had been used primarily as a metering pump, i.e., a pump forintroducing a measured quantity of a liquid from a supply reservoir intoa fluid stream, into one suitable for high pressure washingapplications.

The prior art metering pump comprises a crankcase for journaling adriven shaft about a longitudinal axis and a cylinder block having acylinder receiving bore formed therein with the cylinder block beingaffixed to the crankcase housing such that the axis of the driven shaftis at a predetermined angle relative to the longitudinal axis of thecylinder bore. A cylindrical piston is disposed in the cylinder bore andis affixed to the driven shaft by means of a connecting pin and aspherical bearing. Because of the angle at which the axis of the pistonis out of alignment with the axis of the driven shaft, as the drivenshaft is rotated, the piston both rotates and reciprocates within thecylinder. A suction port is formed through the cylinder block on oneside surface thereof while the discharge port is located on adiametrically opposite surface of the cylinder block. The piston isappropriately formed to provide a pocket which sweeps past the suctionport to thereby pick up a charge of water and then as the piston rotatestoward the discharge port, the reciprocating motion of the pistonincreases the pressure on the fluid until the pocket becomes exposed tothe discharge port. Such a pump design offers the advantage of obviatingthe need for inlet and outlet flow control valves.

Examples of the prior art rotating/reciprocating piston-type pump aredescribed in U.S. Pat. Nos. 3,168,872; 2,517,645 and 1,244,160. Suchpumps have typically been designed to operate at low flow rates andrelatively low pressures which, while satisfactory for meteringapplications, are wholly insufficient for a portable, high pressurespray wash application. To achieve adequate flow rates for high pressurewashing, it is desirable to drive the pump at relatively high RPM, e.g.,about 10,000 rpm. Likewise, to achieve a pump discharge pressure ofabout 1,000 psi, a prime mover of at least 1.5 horsepower is dictated.Keeping in mind that size, weight and cost are important constraints,there are stringent limitations imposed on the pump's stroke volume and,hence, the need for operating at high rpm. The high discharge pressuredesired coupled with the relatively small pump size and the inherentimbalance of forces acting on the piston as it rotates to alternatelyexpose and block the suction and discharge ports presents a real problemin maintaining the piston centered within the cylinder so as to avoidscraping and galling of the walls of the cylinder bore and of the pistonitself. Likewise, the unbalanced pressures makes it somewhat difficultto create seals which will hold up over long periods of use.

Another problem encountered when it is desired to operate a prior artpump of the type disclosed in the aforereferenced patents at high rpmrates is that of maintaining adequate lubrication of the bearing used tooperatively couple the piston to the pump's driven shaft. Theconventional mode of lubrication for a metering pump operated atrelatively low rpm rates is to fill the crankcase housing with oil andthen provide adequate seals between the cylinder wall and the piston toinsure that the liquid being pumped does not flow into the crankcase tocontaminate the oil. It is found that when this lubrication approach isattempted in a positive displacement pump of the type underconsideration driven at 10,000 rpm, a significant loss in pumpefficiency results due to the work involved in moving and churning theoil within its crankcase. Also, with the high pressures desired, thedifficulty in providing an effective oil seal which will hold up overprolonged periods of use is difficult and expensive to attain. At highrpm and pressures typical of the present invention, pressure pulsationsmay cause problems because of excess stresses in the pump or attachedhose and excess noise.

OBJECTS

It is accordingly a principal object of the present invention to providean improved positive displacement pump of the type having a rotary andreciprocating piston for use in high pressure/high flow rateapplications.

Another object of the invention is to provide a positive displacementpump of the type described in which the unbalanced side forces acting onthe piston in prior art reciprocating/rotary piston pumps areeffectively neutralized.

Still another objective of the present invention is to provide effectivemeans for pulsation suppression.

A still further object of the invention is to provide a positivedisplacement pump of the type described with an improved lubricationsystem allowing less expensive lubrication seals to be used whilesimultaneously reducing the work or energy involved in moving thelubricant.

SUMMARY OF THE INVENTION

The foregoing objects and advantages of the invention are achieved byproviding a pump housing which includes a crankcase defining a hollowchamber and a contiguously disposed cylinder block. The cylinder blockincludes a longitudinal cylindrical bore of a predetermined diameter anda pair of oppositely oriented ports which extend laterally through theblock to communicate with the cylindrical bore. A shaft is journaled forrotation in the crankcase where the shaft includes a central axis whichis at a first predetermined angle to the central axis of the cylindricalbore formed in the cylinder block. The shaft supports a sphericalbearing within the hollow crankcase chamber and it is offset radiallyfrom the central axis of the shaft. An elongated cylindrical pistonhaving a pin member extending laterally from a side surface thereofproximate a first end is arranged to fit into the cylindrical bore inthe cylinder block when the pin on the piston is journaled for rotationin the spherical bearing. The laterally extending pin is canted from theperpendicular relative to the longitudinal axis of the piston and thisserves to eliminate pin loading induced side forces on the piston. Thepiston also includes a longitudinal bore extending inwardly from thesecond end thereof and it has a timing window formed through its surfaceat a location which is between the first and second ends and whichcommunicates with the longitudinal bore in the piston. The timing windowis so located that it is swept passed the oppositely oriented portsformed through the cylinder block when the shaft is rotated.

Disposed within the crankcase and surrounding the spherical bearing is alubrication cup which is affixed to the shaft and therefore rotatablewith it. The cup contains a lubricant of high viscosity, e.g., a grease,and when the shaft rotates at high speed, centrifugal force causes thegrease to impinge on the spherical bearing and is contained within thelubrication cup obviating the need for the type of oil seals that areotherwise required.

Pulsation dampeners may be affixed to the cylinder block in a positionto overlie the discharge port for reducing the pressure surges in thewater leaving the exit port. A second pulsation dampener may also beaffixed to the cylinder block in overlaying relation relative to thesuction port. In either event, the pulsation dampeners are designed soas to be closely coupled to their respective port, thus reducing thefluid inertance of the system.

DESCRIPTION OF THE DRAWINGS

The foregoing features, objects and advantages of the invention willbecome apparent to those skilled in the art from the following detaileddescription of a preferred embodiment, especially when considered inconjunction with the accompanying drawings in which like numerals in theseveral views refer to corresponding parts.

FIG. 1 is a side elevation of the positive displacement pump comprisingthe preferred embodiment of the invention;

FIG. 2 is a cross-sectional view taken along the line 2--2 in FIG. 1;

FIG. 3 is an end-view of the drive shaft end of the pump assembly ofFIG. 1;

FIG. 4 is a cross-sectional view taken along the line 4--4 in FIG. 1;and

FIG. 5 illustrates an alternative design for a pulsation dampener to beused with the pump arrangement of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIGS. 1 and 2 of the drawings, the pump of the presentinvention is indicated generally by numeral 10 and is seen to include ahousing 12 of generally rectangular cross-section and which may beformed from a metal such as aluminum or a suitable plastic such as aglass-filled polypropylene of the type sold by the Dupont Corporationunder the trademark, Rynite®. A glass-filled Nylon® plastic may also beused. One such material is GRZ, which is the acronym for GlassReinforced Zytel®. Depending upon the material employed, the block 12 iseither molded or machined to include a crankcase section 14 whichincludes a hollow chamber 16 and a contiguously disposed cylinder blocksegment 18. The cylinder block 18 includes a longitudinal cylindricalbore 20 of a predetermined diameter and extending through the wall ofthe cylinder block so as to communicate with the bore are a pair ofoppositely oriented ports including a suction portion 22 and a dischargeport 24. If the cylinder block is fabricated from cast aluminum, atubular plastic piston sleeve 25 is recommended for inclusion in thebore 20. However, if the cylinder block is formed from plastic, aseparate sleeve may not be required.

Fitted into an annular recess formed in the crankcase 14 is a set ofbearings 28 for journaling a shaft 30 therein. An end cap 32 is boltedto the end of the crankcase 14 to capture the bearing 28 in position.Alternatively, a spring clip or other means may be used to hold thebearing in place. The centerline of the shaft 30 is identified bynumeral 34 and it is designed to intersect at a predetermined acuteangle with the centerline 36 of the cylindrical bore.

The shaft 30 is seen to include a cylindrical segment 38 which projectsoutwardly from the clamping ring 32 and which is adapted to be coupledto a prime mover, such as an electric motor or an internal combustionengine. The segment 38 is integrally formed with a cylindrical segment40 of a larger diameter which is surrounded by and journaled in thebearing 28. Integrally formed with the segment 40 are a plurality oflugs, as at 42 and 44, which effectively surround a socket formed in theportion of the shaft 30 contained within the crankcase chamber 16.Fitted into a circular aperture formed in the lug 42 is a sphericalbearing assembly 46 which includes a stationary race 48 and a toroidalmember 50 having a spherical outer surface cooperating with the race 48.

As best seen in FIG. 2, fitted into the sleeve 25 in the cylindricallongitudinal bore 20 formed in the cylinder block 18 is a piston 52having a first end 54 disposed in the socket defined by the lugs 42, 44,etc. of the shaft 30 and a second end 56 located proximate the top deadcenter position of the cylinder block 18. The piston is preferably madefrom Type 17-4PH stainless steel which has high strength and harnessproperties. A cylindrical pin 58 is press-fit into a radial bore 60formed through the end portion 54 of the piston 52. It is to beespecially noted that the centerline 62 of the pin 58 is notperpendicular to the centerline 36 of the cylinder 20 or that of thepiston 52 but instead is canted at a predetermined angle relative to thelongitudinal axis of the piston and cylinder. For reasons which will beexplained hereinbelow, the angle at which the pin 58 is canted from theperpendicular is determined by the working radius of the pump, which isthe distance between the center of the spherical bearing 46 and thecenterline 36 of the cylindrical bore 20. The angle in question is suchthat a line perpendicular to the pin 58 drawn from the center ofspherical bearing 46 intersects the centerline of the piston at its end56. In this situation, the pin loading induced side forces exerted onthe piston are eliminated over the entire range of rotation of thepiston within the longitudinal cylindrical bore 20, thus obviating theneed for balancing ports or other means for constraining the tendency ofthe piston to move laterally.

The piston 52 includes a longitudinal bore 64 which extends inwardlyfrom the end 56 thereof such that over its working length, the piston 52can be considered as being tubular. Extending through the side wall ofthe tubular piston 52 so as to communicate with the central bore 64 is atiming window 66. It is aligned on the same side of the piston as theprojecting portion of the pin 58.

Because the timing window is displaced longitudinally from the end 56 ofthe piston a cylindrical surface is present on either side of the windowto provide a bearing surface with respect to the tubular sleeve 25 onboth sides of the window. The pin 58 is journaled within the centralopening of the toroidal spherical bearing 46 as illustrated. Thoseskilled in the art will appreciate that when the shaft 30 is rotated,the piston 52 will also rotate within the cylinder bore 20 and willsimultaneously move in longitudinal reciprocal fashion.

With reference now to FIGS. 1 and 4, an inlet port 68 is provided in thecylinder block 18 whereby a connection can be made between a lowpressure water source and the pump. Likewise, on the opposite side ofthe cylinder block is a discharge port 70 through which the highpressure output from the pump is made to pass.

Bolted or otherwise affixed to the side surface 19 of the cylinder block18 is an inlet or suction side pulsation dampener comprising anelastomeric sheet 74 and a generally rectangular frame member 76defining an opening 78 through the thickness dimension thereof. When thepulsation dampener 72 is affixed to the side surface 19 of the pump, theelastomeric sheet 74 overlays the pump's water inlet port 68 as well asits suction port 22. Being distendable, as water under nominal householdpressure is introduced into the inlet port 68, the elastomeric sheet 74is distended into the opening 78 in the frame 76 allowing the water toflow into the pump's suction port 22 when the window 66 of the piston isin fluid communication with that port during its cycle of rotation.

In a somewhat similar fashion, a discharge port pulsation dampener 80 isoperatively associated with the pump's high pressure outlet port 70 andits discharge port 24. In accordance with the embodiment illustrated inFIGS. 1 through 4, the high pressure pulsation dampener 80 comprisesfirst and second rectangular blocks 82 and 84 each having an arcuatecavity as at 86 and 88 formed in apposed surfaces thereof. Sandwichedbetween the blocks 82 and 84 is fiber reinforced elastomeric sheet 90which effectively separates the chambers 86 and 88 from one another.Fitted into a threaded bore 92 formed through the plate 82 is a one-waygas valve 94 which permits a gas, such as nitrogen, under pressure, tobe introduced into the chamber 86. When inflated to an operatingpressure of about 500 psi, the sheet 90 is forced against the arcuatewall of the cavity 88 through which a pattern of small apertures as at96 are formed. With continued reference to FIG. 4, it can be seen thatthe plate 84 is recessed, as indicated by numeral 98, so that when thesurface 100 of the plate 84 is juxtaposed with the wall surface 21 ofthe cylinder block 18, a cavity is formed which overlays the pump's highpressure discharge port 24 and its outlet port 70. The suction anddischarge pulsation dampeners serve to eliminate the need for excessiveinput power to drive the pump and also act to reduce peak forces onbearings, the drive pin and the piston.

As will be explained more fully hereinbelow, when the shaft 30 isdriven, the piston 52 both rotates and translates reciprocally in thelongitudinal bore 20. When the window 66 sweeps past the pump's inletport 22 which allows the interior cavity of the piston to fill withwater, the rotation will reach a point where the timing window iseffectively sealed by the close tolerance between the piston wall andthe associated cylinder wall or sleeve. During this interval, the pistonmoves in its longitudinal direction (to the right when the pump isoriented as shown in FIG. 2) exerting increasing compressive forces onthe liquid. As the window 66 in the piston reaches and sweeps across thedischarge port 24, the water is discharged under high pressure, firstthrough the series of ports 96 and against the pressurized sheet 90 and,thence, out those same ports 96 and the pump's outlet port 70. Thecompliance of the sheet 90 and the pressurized gas in the chamber 86tends to damp out pressure surges as the pump's piston is driven at highrpm.

By canting the pin 58 at a predetermined angle from the perpendicular tothe piston, the direction of force applied to the piston becomesgenerally concentric with the centerline thereof and, as a result, pinloading induced side forces on the piston are eliminated throughout theentire range of motion of the piston. Moreover, it is now possible tolocate the timing window 66 on the same side of the piston as the pin 58extends from and this has the advantage of placing the piston materialsurrounding the window in compression to thereby eliminate the tendencyfor any cracking to occur at the window corners. This affords thefurther advantage of allowing a reduction in the wall thickness of thepiston without incurring such cracking. Of course, a lighter pistonresults in a significant reduction in the inertia of the piston when itis driven at 8,000-10,000 rpm. The degree to which the pin is canted tothe perpendicular to the piston axis is a function of both piston lengthand the working radius of the spherical bearing.

As is illustrated in the view of FIG. 5, in accordance with anotherembodiment, the high pressure discharge pulsation dampener 80 of FIG. 4may be replaced with a molded plastic dome-like member 102. The dome 102is preferably molded from a high strength, low modulus plastic. Thereare certain Nylon formulations exhibiting an elastic modulus of about100,000 psi and a tensile strength of 16,000 psi. That material, whenproperly, dimensioned in terms of length and cross-sectional area,results in a pulsation dampener with relatively low inertance. Moreover,because the pump of the present invention is intended to operate atrelatively high RPM, the acoustic wavelength of the pressure pulsationsis very short which necessitates a short coupling between the pulsationdampener and the pump's suction and discharge ports.

With reference again to FIG. 2, there is identified by numeral 104 a cupwhich is dimensioned to snap onto the lugs 42, 44, etc. of the shaft 30so as to effectively surround the lugs, the spherical bearing assembly46 and the pin 58 which fits into that spherical bearing. With that cupin place, a small quantity of a thick, viscous lubricant, such asgrease, may be deposited within the cavity formed in the inner end ofshaft 30. When the shaft 30 is driven at high speed, centrifugal forcesact on the grease to propel it radially outward where it becomescontained by the cup 104 with very little of the grease exiting theopening formed in the cup 104 through which the end 54 of the pistonextends. The forces acting on the grease cause it to seep into thespherical bearing, thus lubricating it and the pin contained in thebearing. Whereas prior art pumps of the rotating and reciprocatingpiston-type have typically been lubricated by filling the cavity 16 withoil, the use of the cup 104 which allows grease to be used as thelubricant has been found to materially reduce energy losses which, inthe prior art, can be attributable to the churning of the oil within thecavity 16. In addition, because the lubrication cup 104 effectivelycontains the grease lubricant, it becomes unnecessary to provide an oilseal surrounding the piston at the intersection of the crankcase segment14 with the cylinder block 12. Instead, only a single cup seal as at 106is needed to preclude the flow of the liquid being pumped to theinterior of the crankcase chamber 16. Moreover, it has been foundunnecessary to provide an oil seal around the shaft 38 where it extendsout through the retaining collar 32.

This invention has been described herein in considerable detail in orderto comply with the Patent Statutes and to provide those skilled in theart with the information needed to apply the novel principles and toconstruct and use such specialized components as are required. However,it is to be understood that the invention can be carried out byspecifically different equipment and devices, and that variousmodifications, both as to the equipment details and operatingprocedures, can be accomplished without departing from the scope of theinvention itself.

What is claimed is:
 1. A fluid pump comprising:(a) a housing including acrankcase defining a hollow chamber and a contiguously disposed cylinderblock having a longitudinal cylinder bore of a predetermined diameter;(b) a drive shaft journaled for rotating in the crankcase, the centralaxis of the shaft being at a predetermined angle to the central axis ofthe cylinder bore with the shaft supporting a spherical bearing withinsaid hollow chamber at a location offset radially from the central axisof the shaft; (c) a generally cylindrical cup member having a first openend and a second end having a central opening therein, said cup membersurrounding said spherical bearing and affixed to a portion of the shaftdisposed within the hollow chamber for retaining an effective quantityof a sufficiently viscous grease to provide lubrication to saidspherical bearing when said drive shaft is driven at its operating speedwithout loss of said grease through said first open end and said centralopening; and (d) an elongated cylindrical piston having first and secondends and a pin extending laterally from a side surface thereof proximatesaid first end, said pin being journaled in the spherical bearing whenthe piston extends through the central opening in the second end of thecup member and into the longitudinal cylindrical bore of the cylinderblock.
 2. The fluid pump as in claim 1 wherein when said shaft isrotated at high speeds to drive said piston, said cup member retainslubricating grease in a zone traversed by said spherical bearing.
 3. Thefluid pump as in claim 2 wherein said first end of the cup member clampsonto said portion of the shaft disposed within the hollow chamber androtates with the shaft.
 4. The fluid pump as in claim 2 wherein saidlubricating grease is sufficiently viscous to resist flow when saidshaft is stationary but flows when acted upon by a predeterminedcentrifugal force.
 5. The fluid pump as in claim 1 wherein said portionof said shaft contained within said hollow chamber includes an arcuatewall having a circular aperture therein for receiving said sphericalbearing, said cup member concentrically surrounding said arcuate wall.